(1) Field of the Invention
This invention relates to a semiconductor device including a substrate body made of sapphire, SiC or GaN, etc. and an AlxGayInzN film (x+y+z=1; x,y,zxe2x89xa70) formed directly on the substrate body or formed via a buffer film on the substrate body, a manufacturing method of the same and an epitaxial growth substrate for the same.
(2) Related Art Statement
At the present time, a semiconductor device such as a light emitting diode (LED), a laser diode (LD) or a field effect transistor (FET) is well known. Particularly, in the case of producing such a light emitting diode, an AlxGayInzN film (x+y+z=1; x,y,zxe2x89xa70) is epitaxially grown directly on the substrate body or epitaxially grown via a buffer film on a substrate body made of sapphire, SiC or GaN, etc. Since the AlxGayInzN film has a larger band gap, it can generate and emit a short wavelength light.
FIG. 1 is a cross sectional view showing a light emitting diode structure to emit a blue light having the AlxGayInzN film. In the depicted light emitting diode, a GaN 2 film as a buffer layer is formed on a substrate body 1 made of a C-sapphire crystal (Al2O3) by a MOCVD method at low temperature, and an n-type AlxGayInzN film 3 is epitaxially grown on the GaN film 2 by a MOCVD method. Then, a p-type AlxGayInzN film 4 is epitaxially grown on the n-type AlxGayInzN film 3 by a MOCVD method, and a low resistive AlxGayInzN film 5 is epitaxially grown on the n-type AlxGayInzN film 4 by a MOCVD method. Electrodes 6 and 7 are provided on the n-type AlxGayInzN film 3 and the p-type AlxGayInzN film 5, respectively.
In this case, the n-type AlxGayInzN film 3 is grown with keeping the substrate body 1 and the buffer layer 2 at 1000xc2x0 C. and over for improving the crystallinity and the flatness thereof. Therefore, a heater structure and a heater material having high thermal efficiency are desired in order to heat a given substance uniformly. The buffer layer 2 should be also composed of the above GaN film 2 or an AlN film formed at a low temperature to improve the crystallinity and the flatness of the n-type AlxGayInzN film 3. Moreover, a nitride layer formed at a surface of the substrate body may be employed as the buffer layer.
However, the substrate body may not often be heated to a desired temperature depending on the film growth conditions such as gas pressures and gas flow rates of raw materials. As a result, the n-type AlxGayInzN film 3 cannot have good crystallinity and flatness. Moreover, the crystallinity and the flatness of the n-type AlxGayInzN film 3 may fluctuate due to non-uniform heating of the substrate body.
Particularly, in the case of forming an Al-rich AlxGayInzN (x+y+z=1; xxe2x89xa70.5, y, zxe2x89xa70) film, the above-mentioned matters become conspicuous. The first reason is because a carrier gas (H2, NH3) with raw material gases must be delivered at a fast flow rate of almost 1L/minute or more under a depressurized atmosphere of almost 100 Torr or less, to reduce the collision ratio of the elements of the raw material gases and thus repress, in the gas phase, the reaction between the elements of the Al raw material gas and the N raw material gas.
The second reason is because particularly in the case of forming the above Al-rich AlxGayInzN (x+y+z=1; xxe2x89xa70.5, y, zxe2x89xa70) film, the substrate body is heated to 1100xc2x0 C. or greater, to improve its crystallinity and flatness through lateral epitaxial growth.
When the AlxGayInzN film is formed at the above fast gas flow rate under the above depressurized atmosphere in a CVD apparatus, the degree of heat radiation from a surface of the substrate body increases in the case of heating the substrate body with a heater. Therefore, the heater must be heated to a higher temperature than the desired substrate temperature by 100xc2x0 C. or more. As a result, excess load is applied to the heater, and thus, the heater is degraded and the lifetime is shortened. Moreover, the surface of the substrate body may not be heated uniformly.
It is considered that the heating mechanism of the substrate body by the heater is originated from the thermal conduction due to the direct contact between the heater and the substrate body, the thermal conduction through the atmosphere gas composed of the above carrier gas, and the thermal conduction due to heat radiation. In this case, however, since the AlxGayInzN film is formed under a depressurized atmosphere, the thermal conduction through the atmosphere gas does not substantially contribute the heating mechanism. Moreover, since the substrate body is made of a transparent material such as sapphire and thus does not almost absorb infrared light, the thermal conduction due to heat radiation does not effectively contribute to the heating mechanism. As a result, it turns out that the heating mechanism is originated from the thermal conduction due to the direct contact between the heater and the substrate body. Therefore, if the substrate body is not set on a susceptor of the heater so as to contact the surface of the susceptor entirely, the substrate body is not heated to the desired temperature entirely. Moreover, since the carrier gas including the raw material gases is delivered at the above fast flow rate, the heat radiation is brought about remarkably. Furthermore, the substrate body may be warped during the substrate body heating. Consequently, the substrate body is not heated sufficiently by the heater.
The above phenomena are observed when the AlxGayInzN film is formed on a SiC substrate body or a GaN substrate body. Then, the above phenomena become conspicuous in a visible light-near infrared light range of 500 nm-2000 nm wavelength. As mentioned above, in the past, the surface of the substrate body is not heated uniformly under fast gas flow rate conditions, the depressurized atmosphere or the high film growth temperature-film forming, and thus, the AlxGayInzN film cannot have good crystallinity and flatness. Then, excess load is applied to the heater, and thus, the lifetime of the heater is shortened.
It is an object of the present invention to provide a semiconductor device having, on a substrate body, an AlxGayInzN film (x+y+z=1; x,y,zxe2x89xa70) with good crystallinity and flatness through a small amount of defect.
It is another object of the present invention to provide a manufacturing method of the semiconductor device having the AlxGayInzN film (x+y+z=1; x,y,z,xe2x89xa70) with good crystallinity and flatness through uniform heating of the substrate body.
It is still another object of the present invention to provide an epitaxial growth substrate suitable for the above semiconductor device.
This invention relates to a semiconductor device including a substrate body, at least one AlxGayInzN (x+y+z=1; x,y,zxe2x89xa70) film epitaxially grown directly on the upper surface of the substrate body or epitaxially grown via a buffer layer on the upper surface of the substrate body, and a metal film provided on the lower surface of the substrate body.
In a preferred embodiment of the semiconductor device of the present invention, the substrate body is made of a material having a transmissivity of 50% or more within a wavelength range of 400 nm-800 nm. Moreover, the metal film formed on the lower surface of the substrate body is made of a high melting point metal of almost 1200xc2x0 C. or greater, such as W, Ta, Mo, Ti, Be or Mn.
Moreover, in another preferred embodiment of the semiconductor device of the present invention, an Al-rich AlxGayInzN (x+y+z=1; xxe2x89xa70.5, y, zxe2x89xa70) film is formed on the substrate body. Then, the buffer layer is composed of the AlxGayInzN film (x+y+z=1; x,y,zxe2x89xa70).
This invention also relates to a method for manufacturing a semiconductor device including the steps of:
setting a substrate body with a metal film on the lower surface thereof into a CVD apparatus,
introducing raw material gases with a given carrier gas onto the upper surface of the substrate body; and
heating the substrate body via the metal film, thereby to epitaxially grow at least one AlxGayInzN (x+y+z=1; x,y,zxe2x89xa70) film directly on the upper surface of the substrate body or via a buffer layer on the upper surface of the substrate body.
In a preferred embodiment of the manufacturing method of the semiconductor device, the total gas flow rate is set to 1L/minute or over. Moreover, the interior pressure of the MOCVD apparatus is set to 100 Torr or less. Then, a metal film having a high melting point of almost 1200xc2x0 C. or more is formed on the lower surface of the substrate body. Particularly, the above condition is more suitable for manufacturing the AlxGayInzN film having an Al concentration of 50 atomic % or greater (xxe2x89xa70.5).
This invention also relates to an epitaxial growth substrate comprising a substrate body, at least one AlxGayInzN (x+y+z=1; x,y,zxe2x89xa70) film epitaxially grown directly on the upper surface of the substrate body or epitaxially grown via a buffer layer on the upper surface of the substrate body, and a metal film provided on the lower surface of the substrate body.
In a preferred embodiment of the epitaxial growth substrate of the present invention, the substrate body has a transmissivity of 50% or more within a wavelength range of 400 nm-800 nm. Moreover, the metal film formed on the lower surface of the substrate body is made of a high melting point metal of approximately 1200xc2x0 C. or more such as W, Ta, Mo, Ti, Be or Mn. Then, the buffer layer is composed of the AlxGayInzN film (x+y+z=1; x,y,zxe2x89xa70).
According to this invention, the substrate body is heated via the metal film formed on the lower surface thereof by the heater. Since the metal film absorbs infrared light, the substrate body is heated uniformly by the heat radiation of the metal film, and thus, is heated to a desired temperature efficiently. Therefore, when the AlxGayInzN film (x+y+z=1; x,y,zxe2x89xa70) is formed on the substrate body, it can have good crystallinity and flatness. Moreover, excess load is not applied to the heater, and the lifetime of the heater may be elongated.